Small diameter solid fibers of glass and other thermoplastic materials have been used in a variety of applications including acoustical or thermal insulation materials. When these small diameter glass fibers are properly assembled into a lattice or web, commonly called a wool pack, glass fibers which individually lack strength or stiffness can be formed into a product which is quite strong. The glass fiber insulation which is produced is lightweight, highly compressible and resilient. For purposes of this patent specification, use of the term "glass" is intended to include any of the glassy mineral materials, such as rock, slag and basalt, as well as traditional glasses.
The common prior art methods for producing glass fiber insulation products involve producing solid fibers of glass from a rotary process. A single molten glass composition is forced through the orifices in the outer wall of a centrifuge commonly known as a spinner, producing primarily solid and straight glass fibers. The fibers are drawn downward by a blower. A binder required to bond the fibers into a wool product is sprayed onto the fibers as they are drawn downward. The fibers are then collected and formed into a wool pack.
When forming insulation products of glass fibers, the ideal insulation would have uniform spacing between the fibers and the surface area of the fibers would be maximized. Insulation is basically a lattice for trapping air between the fibers and thus preventing movement of air. The lattice also retards heat transfer by scattering radiation. A more uniform spacing of fibers and an increase in fiber surface area would maximize scattering and, therefore, would have greater insulating capability.
In the production of wool insulating materials of glass fibers, it becomes necessary to use fibers that are relatively short. Long fibers tend to become entangled with each other forming ropes or strings. These ropes create a deviation from the ideal uniform lattice and reduce the insulating abilities of the glass wool. However, short fibers that are straight form only a haphazard lattice, and some of the fibers lie bunched together. It is clear that existing glass wool insulating materials have significant non-uniformities in the distribution of fibers within the product. Thus, the ideal uniform lattice structure cannot be achieved.
Additionally, when using straight fibers it is necessary to add an organic binder material to the fibers. The binder is required to hold the product together by bonding at the fiber to fiber intersections. Not only is the binder itself expensive, but great pains must be taken to process effluent from the production process due to the negative environmental impact of most organic compounds. Further, the binder must be cured with an oven using additional energy and creating additional environmental cleanup costs.
As the number of fibers used in the insulation product is increased, the surface area of the fibers is also increased as well as the insulating capability of the resultant wool product. However, increasing the number of fibers also increases the cost of the product due to the cost of the additional material used. Even small changes in the amount of fiber material used can impact production costs.
In the shipping and packaging of insulation products, high compressibility is preferred. It is desirable to compress the wool for shipping and then have it recover rapidly and reliably to the desired size. Current insulation products are limited in the amount of compression possible while still attaining adequate recovery. When the product is compressed, the binder holds firm while the fibers themselves flex. As the stress upon the fibers increases due to excessive compression, the fibers break.
Attempts have been made in the prior art to produce non-straight solid glass fibers. In a mechanical kink process, glass fibers are pulled from a textile bushing. While still at high temperatures, the fibers are pulled by mechanical means through a series of opposed gears or a crimping device to attenuate and crimp them. The net result is a bundle of kinked glass fibers.
The major disadvantage to mechanical kinking is that the fibers are not conducive to satisfactory glass wool production. Every fiber produced in this manner has a uniform shape, defeating the purpose of the kink, because the glass wool produced does not have a uniform distribution. Further, because the process is non-rotary, it has an unsatisfactory low throughput and the fibers produced are too coarse for wool insulating materials.
Stalego, U.S. Pat. No. 2,998,620, discloses curly (helical) glass fibers of bicomponent glass compositions. Stalego discloses producing staple curly fibers by passing two glass compositions having differing coefficients of thermal expansion through the orifices of a spinner. The glasses are extruded as a solid dual glass stream in aligned integral relationship such that the fibers curl naturally upon cooling due to the differences in their coefficients of thermal expansion. However, Stalego discloses employing the curled fibers in the processing of yarns such as being woven into fabric or included as a reinforcement in fired pottery and clays. Stalego does not disclose the use of curly fibers in insulation products. In addition, Stalego discloses in one embodiment a spinner having vertically aligned compartments separated by vertical baffles around the periphery of the spinner, with alternate compartments containing the different glasses. The patentee teaches that an orifice wider than the baffle is to be drilled where the baffle intersects the spinner peripheral wall. As the orifice is wider than the baffle, the orifice is in communication with both of the vertical compartments on either side of the baffle, and both the A glass and B glass will exit the spinner from the orifice, forming a solid dual glass stream.
Tiede in U.S. Pat. No. 3,073,005 discloses a non-rotary process for making bicomponent curly solid glass fibers. The fibers are made by feeding differing glass compositions to an orifice in side by side contact such that the two glasses are attenuated into a single fiber. Tiede discloses using the glasses in fabric production as well as cushion and floatation materials. Tiede does not disclose insulation products made with curly glass fibers.
Slayter et al. in U.S. Pat. No. 2,927,621 also discloses the production of curly fibers. In Slayter, solid glass fibers of a single glass composition are passed through opposed contoured skirts after the fibers have been softened by hot gases. The fibers then take on the shape of the contour of the skirts. However, the thick, long fibers are unsuitable for insulating materials. Rather, the produced fibers are employed in filtering media, and additionally have a binder applied.
Accordingly, a need exists for an improved wool insulating material with a uniform volume filling nature and a maximized fiber surface area such that the wool insulating material has improved recovery and reduced thermal conductivity, remains cost effective, and can be employed without the use of a binder material. It would also be desirable to produce an improved wool insulating material which has the aforementioned attributes but which can be produced with reduced amounts of fiber material.